Adding Edge Loops Around Airplane Window
Avoid NGons, and avoid Boolean operations, you topology is not quad-dominant and you wont be able to easily add edgeloops anywhere with ngons like those around the windows. in fact you will likely have a hard time doing anything at all with your current model.

Ideally your mesh should be made primarily of faces with four sides, use Ctrl+R to add edge loops, use Ctrl+B to bevel, use E to extrude, and abuse of modifiers.

In your case I am guessing a Mirror modifier would help with symmetry, a Subdivision Surface would help with smoothing/curving, and an array might help with multiple windows.